From the Rotline: How do I prevent swarms of flies in my bin?

While there is nothing wrong with having flies in a bin (and in fact, I implore you to find a bin without a resident fly population) they are often cited as a nuisance by backyard composters. Flies do enrich the bin ecosystem; having a variety of decomposers allows for material to be broken down more efficiently and for a more nutrient-diverse final product. That being said, few composters want to feel like a spelunker disturbing a long-forgotten bat cave upon lifting the lid of their bin.

 While species varies with region and pile inputs, the same general techniques will control any fly population. Instead of preparing for battle when you open your bin to turn it, add water, or new material, try these tips to minimize the presence of flies:

  • Add food scraps to the bin immediately, or keep them in a kitchen scrap collector with air holes that are too small for flies to enter. Adding exposed food to your bin is a sure way to seed a new generation of fruit flies, which assuredly accepted your invitation to lay their eggs in the scraps. If you have nothing short of an infestation of flies in your pile, this is probably the culprit.
  • Build a hot compost pile (wherein temperatures exceed 140°F). This will kill already-present eggs and larvae, and discourage mature flies from establishing. Again, if you are dealing with a serious fly infestation, spiking pile temperature several times is an effective way to control the population.
  • Shred exposed food scraps before adding them to the pile to kill eggs and larvae if you aren’t interested in committing to a hot pile.
  • Bury food scraps in the core of the pile; dumping them on top is a surefire way to get a mouthful of flies upon entry. The pile core is also where temperatures get the highest, so in addition to inaccessibility as a new fly nursery, the food becomes an inhospitable nursery for current residents.
  • Turn the pile every 2-3 days to interrupt fly breeding and to discourage mature flies from establishing in the frequently disrupted material.
  • Keep a layer of browns on top of the pile to dissuade flies from hanging out in the upper strata of the bin. Try burlap, cardboard, or newspaper for easy access to pile contents below.

Happy Composting!